Is this a borrowed neutral ?

[novice]

Hello All

I wonder if someone has the time to respond to this. Hoping no one says get an electrician )

21 way rcbo board. One circuit apparently feeds two 2-way led lamps in the garage (next to the CU). Its black neutral wire has just been cut off and left as a "dead end" within the CU. I turn off the rcbo remove both circuit wires. Using a wandering lead from one of the two lamps, I get connectivity between the red wire at the lamp and the red wire removed from the rcbo as expected. However I get zero connectivity between the neutral black wires (after stripping back a little plastic to expose copper). I do get connectivity between the neutral at the lamp and the neutral bar in the CU.

So apart from asking for confirmation that is a borrowed neutral, to find which circuit its getting it from I presume I can isolate each 6 amp circuit in turn and test for continuity from my lamp's neutral wire? The next question is what to do when I find it. Assuming both radials are tiny which they are likely to be (the one in question only has two led lamps on it!) does having two radials entering a single RCBO in itself cause a c1 or c2 within an eicr ?

 

[Fleeting]

So to read through the smog do you have two circuits on two rcbos or two circuits into one rcbo with one neutral cut out or, am I misreading what you are saying.

 

[poni]

I turn off the rcbo remove both circuit wires.

it should be this rcbo that has the neutral to the garage, as for why and how i would need to be on site to tell you more

 

[UNG]

Your description is rather confusing, may be a bit of background as to why you testing the installation would give some indication of what you are trying to achieve
Is this a new CU you are installing and the lighting circuit RCBO is tripping
or
do the lights on the circuit not work and you are trying to locate the problem
or
as you mention EICR coding are you doing an EICR

What level of electrical experience or training do you have and what test equipment are you using

Crystal ball electrical repairs are not easy to do even with a good description and pictures and unfortunately there are times when the only fix is to get an electrician on site to fix it

 

[Murdoch]

If you are doing an EICR it is an FI

 

[SPECIAL LOCATION]

All cables fed from the same protective device are the SAME circuit..

The number of protective devices defines how many circuits you have, Not the number of cables..
e.g. 2x 6amp MCBs (or RCBOs) with one supplying 2x T&E, and the other supplying 3x T&E, are just TWO circuits,
even though 5 T&E's leave the CU.

A radial circuit can have numerous branches which may be at junction boxes, accessories OR the supplying protective device.
(a branch off a circuit does NOT create a new circuit.)

A "borrowed", (or more correct "shared") neutral, is where TWO circuits (i.e. protective devices) can supply the same piece of cable.
Have you proved that your unknown neutral can become energised via more than one protective device?

Multiple conductors into a single protective device does not constitute any code on an EICR..
unless the CSA are too small, or they cannot be securely clamped into the cable termination because there are too many conductors in there..

Your description is a bit too vague to figure out exactly what you have or not?

 

[novice]

Yes I apologise I'm going to have to own up and explain what I'm doing otherwise I agree its difficult to understand. I wanted to reduce the chance of being told off )

Anyway, for my sins, I decided to run a new 40amp circuit in 10mm t+e from my existing Wylex board which you can see below. That goes into a changeover unit and on to the new "emergency fuseboard" and the idea is I will add a portable generator into that shortly. I know I'm not allowed to do it so my tin hat is well and truly on.

So the plan was to move all the lighting circuits and an existing 16A (15A in old money) boiler circuit. Once the Wylex lid was off I started to see just how many circuits were doubled and trebled up. In fact one 5a circuit had 4 lighting radials attached! So given the size of the new RCBO Fusebox board, I thought I'd take the opportunity and separate them into their own RCBOs.

Everything was going fine as I migrated the circuits one by one until I got to this garage circuit apparently consisting of a pair of 2 way lights. When moved from the old Wylex mcb into separate RCBOs, I found the circuit tripped as soon as I tried to switch on the lights. That was when I started (dead) testing and could see that those two lights had neutrals that were not connected to its corresponding circuit at the CU so figured they must be getting the neutral from another circuit.

Note I obviously extended some of the circuits from within the Wylex metal box (its that old). I crimped most until I ran out of heatshrink then used waygos. All the white cable flapping around outside was like that. I guess I'm making excuses for myself - cut me down !

 

[Fleeting]

Every final circuit should be protected by an individual protective device this is a requirement in BS7671. You are correct that multiple final circuits require individual circuit protection and it appears two of these final circuits have crossed neutral conductors.

 

[Murdoch]

Be careful here. 2 cables into one OCPD = 1 circuit

Some muppets disagree but they are very wrong

 

[Sharpend]

Not sure it’s very wise putting the CU below a waste pipe? A leak will make for an interesting show.

 

[Fleeting]

Be careful here. 2 cables into one OCPD = 1 circuit

Some muppets disagree but they are very wrong

Not to get into an argument but I disagree.

 

[Murdoch]

Not to get into an argument but I disagree.

32A MCB. RFC . Spur at OCPD = 3 cables = 1 circuit

 

[Fleeting]

32A MCB. RFC . Spur at OCPD = 3 cables = 1 circuit

Yes a predictable retort as I said I am not going to argue the point.

 

[binky]

Yes I apologise I'm going to have to own up and explain what I'm doing otherwise I agree its difficult to understand. I wanted to reduce the chance of being told off )

Anyway, for my sins, I decided to run a new 40amp circuit in 10mm t+e from my existing Wylex board which you can see below. That goes into a changeover unit and on to the new "emergency fuseboard" and the idea is I will add a portable generator into that shortly. I know I'm not allowed to do it so my tin hat is well and truly on.

So the plan was to move all the lighting circuits and an existing 16A (15A in old money) boiler circuit. Once the Wylex lid was off I started to see just how many circuits were doubled and trebled up. In fact one 5a circuit had 4 lighting radials attached! So given the size of the new RCBO Fusebox board, I thought I'd take the opportunity and separate them into their own RCBOs.

Everything was going fine as I migrated the circuits one by one until I got to this garage circuit apparently consisting of a pair of 2 way lights. When moved from the old Wylex mcb into separate RCBOs, I found the circuit tripped as soon as I tried to switch on the lights. That was when I started (dead) testing and could see that those two lights had neutrals that were not connected to its corresponding circuit at the CU so figured they must be getting the neutral from another circuit.

Note I obviously extended some of the circuits from within the Wylex metal box (its that old). I crimped most until I ran out of heatshrink then used waygos. All the white cable flapping around outside was like that. I guess I'm making excuses for myself - cut me down !

That old Wylex boad is the sort of 'rats nest' of wiring we all love so much! .

Given what you have found, I think I would be inclined to rewire the garage light feed. There are ways of testing to fing which cct the neutral has been borrowed from, but as that involves working live, I'm not inclined to give such advice as it's 'naughty' and potentially dangerous. The less dodgy option is complete the rest of the work, leaving those 2 cables disconnected, as see what else doesn't work other than the garage lights.

 

[UNG]

Yes a predictable retort as I said I am not going to argue the point.

So why make the comment if you don't want to debate the point

 

[Murdoch]

Yes a predictable retort as I said I am not going to argue the point.

You can’t say that this senario is 2 circuits.

End of

 

[UNG]

Yes I apologise I'm going to have to own up and explain what I'm doing otherwise I agree its difficult to understand. I wanted to reduce the chance of being told off )

Anyway, for my sins, I decided to run a new 40amp circuit in 10mm t+e from my existing Wylex board which you can see below. That goes into a changeover unit and on to the new "emergency fuseboard" and the idea is I will add a portable generator into that shortly. I know I'm not allowed to do it so my tin hat is well and truly on.

So the plan was to move all the lighting circuits and an existing 16A (15A in old money) boiler circuit. Once the Wylex lid was off I started to see just how many circuits were doubled and trebled up. In fact one 5a circuit had 4 lighting radials attached! So given the size of the new RCBO Fusebox board, I thought I'd take the opportunity and separate them into their own RCBOs.

Everything was going fine as I migrated the circuits one by one until I got to this garage circuit apparently consisting of a pair of 2 way lights. When moved from the old Wylex mcb into separate RCBOs, I found the circuit tripped as soon as I tried to switch on the lights. That was when I started (dead) testing and could see that those two lights had neutrals that were not connected to its corresponding circuit at the CU so figured they must be getting the neutral from another circuit.

Note I obviously extended some of the circuits from within the Wylex metal box (its that old). I crimped most until I ran out of heatshrink then used waygos. All the white cable flapping around outside was like that. I guess I'm making excuses for myself - cut me down !

That Wylex looks like the creation of a future fault finding nightmare in progress as none of the cables look to have any identification markers on them

With a bit of prior planning and some testing that Wylex should have been taken out IMO and been replaced by the new CU. Yes it can be a daunting prospect when faced with a mess like that Wylex especially if you have limited experience but with a methodical plan it can be made a lot easier and the finished job is more satisfying

Looking at your configuration of the new CU it seems at odds with most manufacturers instructions regarding the grouping of potentially high load RCBO's due to the cumulative thermal effects that may effect there expected operation

 

[Fleeting]

You can’t say that this senario is 2 circuits.

End of

I never suggested that at all.

 

[brightspark]

Could be wrong as picture not overly clear but are the new fusebox rcbos A type or a AC type?

 

[SPECIAL LOCATION]

In case anyone is in any doubt: BS761, Definitions, Part2, page 31:

Circuit:
An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s),

No mention of the number of conductors connected...

Just simply 1x Fuse / MCB / RCBO suppling an assembly of other various bits = 1x circuit.